Is it time to get a new doctor?

My mother has been taking Prednisone for a couple months now and last month she started having difficulty walking. Now her legs have attrophied to the point where she can barely walk. She is so weak. The doc says its dehydration from the massive sweating she does and says Prednisone has nothing to do with the legs or weakness but I keep reading that both are symptoms. Is it time to get a new doc? Has this happened to anyone else?